Coal Energy for the Future (1995) / Chapter Skim
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7 ELECTRIC POWER GENERATION
7 ELECTRIC POWER GENERATION
Pages 113-149
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From page 113... ...
These efforts include R&D on components that are engineered and designed to operate in an integrated fashion in advanced power generation systems. For example, IGCC electric power systems include components such as advanced coal gasifiers, hightemperature gas cleanup systems, and advanced gas turbines.
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From page 114... ...
State of the Art The overall efficiency of a pulverized coal power generation cycle is affected by many factors, including the thermodynamic cycle design, steam conditions (temperature and pressure) , coal grind, combustion air-to-fuel ratio, fuel mixing, air leakage into the system, cooling (condenser)
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From page 115... ...
Typical capital costs of modern U.S. subcritical pulverized coal plants equipped with an FGD system range from about $1,100 to $1,500/kW, with typical electricity costs of about 40 to 55 mills/kWh.i Current Programs The DOE program to improve pulverized coal-based power generation systems builds on several aspects of current pulverized coal power generation technology that are commercial or near-commercial, including: .
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From page 116... ...
116 Cal Cal V)
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From page 117... ...
Thus, the turbine is not directly exposed to corrosive and abrasive coal combustion products. The ceramic heat exchanger tubes will allow clean filtered air from the gas turbine compressor to be heated to the turbine inlet temperature, eliminating the need for complex fuel preparation from pulverized coal (LaHaye and Bary, 1994~.
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From page 118... ...
An example of the technical challenges facing DOE is illustrated by the heat exchanger requirements for the EFCC system. Experimental studies in the 1940s on open-cycle, indirectly fired gas turbines using metallic heat exchangers did not allow sufficiently high turbine inlet temperatures for economic power production (Orozco, 1993~.
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From page 119... ...
Findings Pulverized coal combustion systems are an established and mature technology for power generation, with comparatively limited opportunity for further performance enhancements based on a simple Rankine steam cycle relative to advanced combined-cycle systems. Thus, the market niche for the LEBS system is not clear.
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From page 120... ...
If the PFBC unit exhaust gas can be cleaned sufficiently without reducing its temperature (i.e., by using hot gas cleanup systems) , additional cycle efficiency can be achieved.
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From page 121... ...
This PFBC testing will evaluate the integration of all of the components in the PFBC system, with emphasis on the integration of hot gas cleanup ceramic filters and gas turbines (DOE, 1993a)
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From page 122... ...
To further enhance its commercial application, manufacturers need to refine the technology to achieve lower capital costs compared with modern pulverized coal (PC) plants, improved environmental performance, and improved operating efficiency.
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From page 123... ...
One of the key performance and cost uncertainties for advanced PFBC systems is the development of hot gas cleanup technology. Reliable hot gas particulate cleanup plus advanced (1370 °C t2500 °F]
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From page 124... ...
Based on current environmental control capabilities, IGCC offers a coal-based power technology with low emissions, high thermal efficiency, and the potential for phased construction that is, building simple-cycle natural-gas-fired combustion turbines first, then converting to combined-cycle, and finally adding coal gasification as gas prices increase or gas availability deteriorates. Future advances in gasification-based power production are linked to increases in gas turbine firing temperature, hot gas cleanup of the fuel gas, coproduction of both chemicals and electricity, improved gasifies designs, and integration of gasification with advanced cycles and fuel cells.
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From page 125... ...
. Table 7-3 summarizes the performance and economics for a hypothetical SOO-MW first-generation IGCC plant employing a state-of-the-art, oxygen-blown, entrained-flow gasification process to provide fuel gas to advanced combustion turbines.
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From page 126... ...
Future improvements to the economics of IGCC, therefore, are linked mainly to development of advanced gas turbines with firing temperatures over 1370 °C (2500 °F) and secondarily to development of reliable hot gas cleanup schemes.
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From page 127... ...
The key issue for these technologies is the high capital cost and its impact on economic competitiveness. Gasification is an enabling technology that allows the use of very high efficiency energy conversion devices such as high-temperature gas turbines and fuel cells for power production in combined-cycle systems.
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From page 128... ...
MW (net) Startup SEP, Buggenum, Netherlands ELCOGAS, Puertollano, Spain RWE, KoBra, Hurth, Germany Shell entrained Oxygen-blown Cold gas cleanup Siemens V94.2 gas turbine PRENFLO entrained Oxygen-blown Cold gas cleanup Siemens V94.3 gas turbine HT Winkler fluid bed Air-blown Cold gas cleanup Siemens V94.3 gas turbine '1 ~253 January 1994 43 300 Mid- 1996 43 3 1 2 Post-2000 Source: Wolk and Holt (1994)
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From page 129... ...
It is anticipated that the scale will be increased to 10 kW within one year. Fuel cells integrate readily with coal gasifiers.
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From page 130... ...
This is generally considered feasible, with technological advances already planned for the fuel cell and gas cleaning subsystems within the plant. Technical Issues, Risks, and Opportunities IGFC will not materialize for utility-scale electricity generation until the fuel cells are first used commercially as small-scale distributed generators on natural gas.
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From page 131... ...
The FY 1994 budget authorization for fuel cells RD&D which is now in the natural gas program was $51.8 million. DOE is supporting technology and demonstrations of MCFC by two manufacturers at approximately $30 million/year, with EPRI and GRI collaborating at approximately $5 million/year each.
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From page 132... ...
Therefore, planned DOE support of balance of plant cost reduction development is the logical next step in fuel cell technology development, since these costs are larger than the fuel cell stack costs. Future development of coal-based IGFC systems will depend on the success of current gas-based technology and on the resolution of key technical issues, particularly the types and levels of contaminants in coal-derived fuel gas that must be controlled.
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From page 133... ...
At the same time, the thermal efficiency advantage of MHD systems has been eroded by more recent developments in other coal-based systems employing advanced gas turbines, fuel cells, .
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From page 134... ...
COMBUSTION TURBINES Background The combustion turbine is the key power generation component in most advanced coal-based systems. The turbine system consists of a compressor to take combustion air from atmospheric pressure to a pressure of 8 to 16 atmospheres; a combustor burning a fossil fuel (natural gas, light refined petroleum fractions, or coal-derived fuel gas)
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From page 135... ...
, heavy-frame, and aeroderivative combustion turbines burning natural gas being sold now or expected for delivery in the mid- 1990s. If the feed gas has been cleaned to a level that will meet air quality standards, oxides of nitrogen (NOX)
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From page 136... ...
A major uncertainty for coal-based applications is the level of fuel gas cleanup needed to protect such advanced turbine designs. Other technical issues facing application of combustion turbines in advanced coal-based power generation include · use of medium- and low-Btu fuel gas in combustors, and the effect of gas composition and variability on combustion efficiency and emissions; · corrosion and/or deposition on turbine blades; · integration of coal gasification with novel combustion turbine thermodynamic cycles; and · potential for catalytic combustion (low NOX)
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From page 137... ...
Current Programs DOE's Advanced Turbine Systems (ATS) program housed in the natural gas program of the Office of Fossil Energy is a major effort to develop and design high-efficiency combined-cycle combustion turbines.
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From page 138... ...
Continued combustion turbine technology improvements and advanced cycles development on natural gas also will benefit the economics of future coal-based systems such as IGCC, PFBC, and IFC designs. With respect to coal-based applications, key issues and uncertainties include fuel gas cleanup requirements for advanced turbine designs and the design and integration of turbine systems that can optimally accommodate evolution from natural gas to coal gas firing.
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From page 139... ...
In gasification-based systems, nitrogen in the fuel gas stream typically occurs as ammonia, which is converted to NOx upon combustion in the gas turbine. Cold gas cleanup systems remove most of the ammonia prior to combustion, thus lowering potential NOx emissions, while current hot gas systems do not.
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From page 140... ...
In the future, however, waste minimization is expected to become increasingly important in response to new economic and environmental pressures. State of the Art Recent trends in particulate, SO2, and NOX emission reductions achievable with current technology for pulverized coal-fired power plants were addressed in Chapter 3 (see Figure 3-2~.
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From page 141... ...
In addition to the emission control systems above, advanced systems employing hot gas cleanup and in-bed desulfurization are being developed. For PFBC systems, the current state of the art for sulfur removal employs a circulating PFBC designed to achieve SO2 removal efficiencies of 95 percent or more (DOE, 1994a)
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From page 142... ...
Hot gas particulate removal from PFBC and IGCC gas systems also is under development. These devices can be viewed as an integral component of the power generation system rather than as an environmental control technology, since they serve the critical function of removing particles and alkaline materials from the fuel gas to protect the gas turbine from erosion and corrosion.
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From page 143... ...
. Several advanced flue gas cleanup systems being demonstrated in the CCT program produce by-product sulfur or sulfuric acid, as do the hot and cold gas cleanup systems employed with coal gasifiers.
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From page 144... ...
Similarly, the extent to which vapor-phase emissions such as mercury, chlorides, and selenium will have to be controlled is not yet clear; technologies to control these emissions may well be needed in the near future. Should that be the case, an additional risk of hot gas cleanup systems is their uncertain capability to control emissions of air toxics, since they presently do not remove vapor-phase species.
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From page 145... ...
Current DOE Programs The Control Technology program in the Office of Fossil Energy is divided into four program components: Flue Gas Cleanup, Gas Stream Cleanup, Waste Management, and Advanced Research. As noted in Chapter 2, DOE has established incremental emission control goals for its Advanced Power Systems program (Table 2-3)
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From page 146... ...
The final component of the Control Technologies Program is Advanced Research. The emphasis in this part of the program is on fundamental hot gas cleanup methods such as ceramic filter and membrane research.
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From page 147... ...
1994b. Summary of Hot Gas Desulfurization and Direct Sulfur Recovery Process Activities in the Fossil Energy Advanced Power Systems Program.
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From page 148... ...
Paper presented at the Joint Contractors Review Meeting, FE/EE Advanced Turbine Systems Conference, FE Fuel Cells and Coal-Fired Heat Engines Conference.
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From page 149... ...
1994. Fluidized Bed Combustion for Coal-Fired Plants: Environmental Performance.
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